2015 New York Laws
MDW - Multiple Dwelling
Article 6 - (Multiple Dwelling) CONVERTED DWELLINGS
Title 1 - (172 - 179) LIGHT AND AIR
178 - Lighting and ventilation of stairs.

  178. Lighting and ventilation of stairs. Where the stair and public
  halls are not provided on each story with windows opening to  a  street,
  yard  or  court,  a  skylight  equipped with ridge ventilators having an
  opening of forty square inches or more shall be  provided  in  the  roof
  over  the  stair,  except  as  otherwise  provided  in  paragraph  g  of
  subdivision three of section one hundred seventy-one. The glazed roof of
  such skylight shall not be less in area than nine square feet  nor  less
  than two feet in its least dimension, provided the ventilating and glass
  areas in such skylight are not less than herein required; except that in
  dwellings   converted   before   April   eighteenth,   nineteen  hundred
  twenty-nine, where a skylight smaller than  such  prescribed  dimensions
  was  in  existence on such date, no structural change shall be required,
  but a ventilating skylight fitting the existing skylight opening in  the
  roof beams shall be deemed sufficient.